Preventing flash rust...

[rustybronco]

http://www.eng-tips.com/viewthread.cfm?qid=324397

Another treasure trove of digestible reading material...

I was responsible for the manufacture of M42 high speed steel at Crucible Materials Corporation for 10 years, and handled many different types of customer complaints and application issues. I never had a customer complain about corrosion issues with this grade, either during manufacturing or in application. This makes me wonder if you are exposing the material to chlorine during the manufacturing process. Are you mixing your own cutting fluids? Are you using city water for this purpose? During the summer months, municipalities often spike their water supplies with chlorine in order to kill bacteria that can otherwsie grow and spread disease. If you don't actively filter this excess chlorine out of the water (using charcoal filtration for example) before using it to mix your cutting fluids for machining, it will expose the M42 to a known corrosion agent.

Maui

Hebe7671

Ok, I did a few trial runs of washing the parts in DI water afrer the machining operations and found that it greatly reduced, but did not completly eliminate, the corrosion issue. With the DI water, there was no flash rust but after a few hours a few small spots of rust could be seen.

http://en.wikipedia.org/wiki/Purified_water

[rustybronco]

http://www.homedepot.com/catalog/pdfImages/3f/3fad4c2b-34e1-4f45-8410-f64dd7feea48.pdf

Phosphoric acid {Orthophosphoric acid} 7664-38-2 CAS # 35.0 -45.0 %

By my calculation it's 38% by specific gravity. (Specific Gravity (Water = 1): 1.25)

http://www.handymath.com/cgi-bin/phostble.cgi?submit=Entry

http://www.finishing.com/512/95.shtml

This is a common problem.

Have you checked your incoming rinse water quality? Tap water can vary from place to place, and it can cause problems. Salts (**chlorine is one) and very high/low pH can accelerate flash rusting. If your tap water is bad, a simple in-line DI system (the cartridge type) can work wonders.

Another solution is to run your final rinse at a slightly acidic pH. Some people will actually use a very small amount of the phosphate concentrate to keep a slightly acidic tank.

Is this a new problem? It looks like your Phosphate concentration is too high and your immersion is too long. Try 2.0 to 2.5 and about a minute to a minute and a half, keep the pH at about 5.5 to 6.0 range and see if that helps. You didn't say whether or not the phosphate stage is heated, if it is keep the temp under 110 degrees. The ppm of the final rinse should be as low as possible, in the less than 50 range.

In order to reduce or prevent flash rusting, it appears to me, you need to use De-ionized water with a 2~2.5% percent concentration of phosphoric acid ( 7~8 oz of prep & etch per gallon of water), keep the rinse solutions temp below 110° F followed by forced air drying the inside of the fuel tank.

[Crankthat]

The forum looks like a treasure trove indeed!
Thank you for sharing.

[rustybronco]

Now all that's needed is to find the best method of rust removal that would preserve as much as what the original metal looked like. (If that's even possible)

[83_450E]

Now all that's needed is to find the best method of rust removal that would preserve as much as what the original metal looked like. (If that's even possible)

http://www.instructables.com/id/Electrolytic-Rust-Removal-aka-Magic/

behold the magic bucket of fizzy bubbly.